A conventional air conditioner apparatus for a vehicle (patent documents 1 to 3) is equipped with actuators (servomotors or the like), electronic control circuits and an electronic control unit (ECU). The actuators drive various doors such as an air mixing door provided in an air conditioner unit to rotate by output shafts thereof, respectively. The control circuits detect present positions of the output shafts of the actuators and control the actuators based on the detected present positions, respectively, thereby to drive each actuator to the target stop position. The ECU communicates with the control circuits and transmits the target stop position of each actuator to the corresponding control circuit.
If the actuator operates beyond a normal operation range in its operation without stopping for some reason, the air mixing door or a mode switching door hits a wall such as a duct of the air conditioner apparatus. The actuators, which use pulse encoders for detecting the present positions as disclosed in the patent documents 1 to 4, cannot detect the absolute values of the present positions. If the present position cannot be acquired after the turn-on of electric power or for some reasons, original position detection control is performed to fix the present position of the actuator. In this control, if the actuator is driven to rotate in reverse from the original position, the air mixing door or the mode switching door will hit the wall. If the air mixing door or the mode switching door hits the wall frequently or the actuator is continued to be driven while hitting the outside door, the wall of the air conditioner unit will be deformed or an unnecessary current will flow in the actuator. The electronic control unit therefore performs control to stop the actuator by detecting hitting of the wall.    Patent document 1: JP 2007-314119A    Patent document 2: JP 2005-112293A (US 2005/0077858)    Patent document 3: JP 2006-298170A    Patent document 4: JP 9-201084A
According to the conventional apparatus, it takes some time for the electronic control unit to transmit a control command for stopping the servomotor to the servomotor control circuit after the present position of the servomotor become unavailable for some reason or the abnormality of the servomotor is detected by the electronic control unit based on the operation of the servomotor outside an operation range limit. It is also difficult to determine the abnormality instantaneously because the electronic control unit and the motor control circuit perform communications regularly. This problem becomes more remarkable if the number of the servomotors (the number of the servomotor control circuits) increases, because a communications interval and processing time necessarily become long.
It is also of disadvantage that no device is provided, which stops the servomotor, if the electronic control unit cannot control the servomotor because of abnormality arising in communications lines or communications circuits.